Illustrated in copending applications U.S. Ser. No. 09/770,159, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, is an organic light emitting device, comprising in an optional sequence
(i) a substrate;
(ii) a first electrode;
(iii) a mixed region comprising a mixture of a hole transport material and an electron transport material, and wherein this mixed region includes at least one organic luminescent material;
(iv) a second electrode;
(v) a thermal protective element coated on the second electrode; wherein one of the two said electrodes is a hole injection anode, and one of the two said electrodes is an electron injection cathode, and wherein the organic light emitting device further comprises;
(vi) a hole transport region, interposed between the anode and the mixed region, wherein the hole transport region optionally includes a buffer layer; and
(vii) an electron transport region interposed between the second electrode and the mixed region; and U.S. Pat. No. 6,479,172, the disclosure of which is totally incorporated herein by reference, is an electroluminescent device comprised of a first electrode, an organic electroluminescent element, and a second electrode wherein said electroluminescent element contains a fluorescent hydrocarbon component of Formula (I) 
wherein R1 and R2 are substituents selected from the group consisting of hydrogen, an alkyl, an alicyclic alkyl, an alkoxy, a halogen, and a cyano; Ar1 and Ar2 are each independently an aromatic component or an aryl group comprised of a from about 4 to about 15 conjugate-bonded or fused benzene rings.
The mixed region, the hole transport region including the buffer layer, and the electron transport region reduce changes in device luminance and/or driving voltage during device operation, and enable stability in the device luminance and/or driving voltage during device operation for extended periods of time at elevated temperatures, while the thermal protective coating increases the device resistance to shorting at elevated temperatures, and thus improves the thermal durability of the organic EL device.
Illustrated in U.S. Pat. No. 6,492,339 on xe2x80x9cOrganic Light Emitting Devices Having Improved Efficiency and Operation Lifetimexe2x80x9d, filed on Jul. 20, 1999, and U.S. Pat. No. 6,392,250 on xe2x80x9cOrganic Light Emitting Devices Having Improved Performancexe2x80x9d, filed on Jun. 30, 2000, the disclosures of which are totally incorporated herein by reference, are organic light emitting devices (organic EL devices) that, for example, comprise a mixed region including a mixture of a hole transport material and an electron transport material. At least one of a hole transport material region and an electron transport material region can be formed on the mixed region. The stability of the above mentioned organic EL devices disclosed in U.S. Pat. No. 6,392,339 and U.S. Pat. No. 6,392,250 is usually reduced at temperatures above 80xc2x0 C. due, it is believed, to a decrease in the device resistance to shorting and also since, it is believed, to a progressive increase in the driving voltage required to drive a certain current through the organic EL devices. As a result, the operational stability of these devices can be limited to a few hundred hours or less at these high temperatures, and more specifically, at high temperatures in the range of from about 80xc2x0 C. to about 100xc2x0 C. Therefore, these devices are believed to be unsatisfactory in some instances, for applications in which there is desired an operational stability of the organic EL device of at least, for example, several thousand hours at temperatures of, for example, 90xc2x0 C., such as, for example, in some automotive, military or other industrial applications where durability in harsh conditions is necessary.
Also, illustrated in copending U.S. Ser. No. 09/629,163 (D/A0057) on xe2x80x9cAnnealed Organic Light Emitting Devices And Methods Of Annealing Organic Light Emitting Devicesxe2x80x9d, filed Jul. 31, 2000, the disclosure of which is totally incorporated herein by reference, is a thermal annealing method and also annealed organic light emitting devices wherein the device performance is improved by means of thermal annealing.
The appropriate components and processes of the above copending applications may be selected for embodiments of the present invention.
This invention relates to optoelectronic devices and, more particularly, to organic light emitting, or organic electroluminescent (EL) devices. More specifically, the present invention relates to stable organic EL devices, and which devices do not substantially degrade, or possess minimum degradation at, for example, high temperatures, such as 100xc2x0 C., and moreover devices which are not substantially adversely affected by high temperatures. The organic EL devices according to the present invention can be used for various applications, and are especially useful in high temperature technological applications that usually require operating, storing, and/or heating the organic EL device at temperatures above 25xc2x0 C., and more specifically, at temperatures in the range of about 60xc2x0 C. to about 100xc2x0 C.
Tang and Van Slyke disclose electroluminescent devices, reference C. W. Tang and S. A. Van Slyke, xe2x80x9cOrganic Electroluminescent Diodes,xe2x80x9d Appl. Phys. Lett. 51, pp. 913-915, 1987. Since this publication, organic light emitting devices (OLEDs) have attracted attention because of their potential for use in the fabrication of large-area displays, reference J. R. Sheats et al, xe2x80x9cOrganic Electroluminescent Devices,xe2x80x9d Science 273, pp. 884-888, 1996; J. Salbeck, xe2x80x9cElectroluminescence with Organic Compounds,xe2x80x9d Ber. Bunsenges. Phys. Chem. 100, pp. 1667-1677, 1996; and Z. Shen et al., xe2x80x9cThree-Color, Tunable, Organic Light-Emitting Devices,xe2x80x9d Science 276, pp. 2009-2011,1997.
In general, the structure of an EL device 10 is illustrated in FIG. 1. The EL device 10 includes a substrate 12 composed of, for example, glass; a first electrode 14 on the substrate 12; a second electrode 16; and interposed between the first electrode 14 and the second electrode 16 a light emitting region 18 formed of at least one layer comprising an organic luminescent material, such as, for example, a metal oxinoid compound, a stilbene compound, an anthracite compound, a polyfluorene, or a poly(p-phenylenevinylene). One of the electrodes includes a layer comprising at least one material with a high work (typically  greater than 4.0 eV), such as, for example, indium tin oxide (ITO) and functions as an anode, whereas the other electrode includes a layer comprising at least one material with a low work function (typically  less than 4 eV), which can be a metal (such as, for example, Ca or Al), a metal alloy (such as, for example, Mg:Ag or Al:Li) or a metal compound (such as, for example, an alkaline metal halides or oxides), and which functions as a cathode. During operation, an applied electric field causes positive charges (holes) to be injected from the anode, and negative charges (electrons) to be injected from the cathode to recombine in the light emitting region 18 and thereby produce light emission.
A problem common to this type of known organic EL devices is poor thermal stability which usually renders the EL device unsuitable for technological applications that require high durability of devices at high temperatures, and which temperatures are, for example, above about 60xc2x0 C., and specifically, temperatures in the range of about 70xc2x0 C. to about 100xc2x0 C. At these high temperatures, device shorting often occurs leading to high leakage currents, thus rendering the organic EL devices nonfunctional (reference, for example, Zhou et al., xe2x80x9cReal-time observation of temperature rise and thermal breakdown processes in organic LEDs using an IR imaging and analysis systemxe2x80x9d, Advanced Materials 12, pp 265-269, 2000).
Therefore, there is a need to prevent or, at least, to significantly reduce, or minimize the likelihood of the aforementioned prior art shorting of the organic EL device. This advantage is achievable with the organic EL devices of the present invention in embodiments thereof.
An organic EL device can be comprised of a layer of an organic luminescent material interposed between an anode, typically comprised of a transparent conductor, such as indium tin oxide, and a cathode, typically a low work function metal such as magnesium, calcium, aluminum, or the alloys thereof with other metals. The EL device functions on the primary principle that under an electric field, positive charges (holes) and negative charges (electrons) are respectively injected from the anode and cathode into the luminescent layer and undergo recombination to form excitonic states which subsequently emit light. A number of prior art organic EL devices have been prepared from a laminate of an organic luminescent material and electrodes of opposite polarity, which devices include a single crystal material, such as single crystal anthracene, as the luminescent substance as described, for example, in U.S. Pat. No. 3,530,325. However, these devices are believed to require excitation voltages on the order of 100 volts or greater.
An organic EL device with a multilayer structure can be formed as a dual layer structure comprising one organic layer adjacent to the anode supporting hole transport, and another organic layer adjacent to the cathode supporting electron transport and acting as the organic luminescent zone of the device. Examples of these devices are disclosed in U.S. Pat. Nos. 4,356,429; 4,539,507 and 4,720,432, wherein U.S. Pat. No. 4,720,432 discloses, for example, an organic EL device comprising a dual-layer hole injecting and transporting zone, one layer being comprised of porphyrinic compounds supporting hole injection, and the other layer being comprised of aromatic tertiary amine compounds supporting hole transport. Another alternate device configuration illustrated in this patent is comprised of three separate layers, a hole transport layer, a luminescent layer, and an electron transport layer, which layers are laminated in sequence and are sandwiched between an anode and a cathode. Optionally, a fluorescent dopant material can be added to the emission zone or layer whereby the recombination of charges results in the excitation of the fluorescent.
There have also been attempts to obtain electroluminescence from organic light emitting devices containing mixed layers, for example, layers in which both the hole transport material and the emitting electron transport material are mixed together in one single layer, see, for example, J. Kido et al., xe2x80x9cOrganic Electroluminescent Devices Based On Molecularly Doped Polymers,xe2x80x9d Appl. Phys. Lett. 61, pp. 761-763, 1992; S. Naka et al., xe2x80x9cOrganic Electroluminescent Devices Using a Mixed Single Layer,xe2x80x9d Jpn. J. Appl. Phys. 33, pp. L1772-L1774, 1994; W. Wen et al., Appl. Phys. Lett. 71, 1302 (1997); and C. Wu et al., xe2x80x9cEfficient Organic Electroluminescent Devices Using Single-Layer Doped Polymer Thin Films with Bipolar Carrier Transport Abilities,xe2x80x9d IEEE Transactions on Electron Devices 44, pp. 1269-1281, 1997. In a number of such structures, the electron transport material and the emitting material are the same. However, as described in the S. Naka et al. article, these single mixed layer organic light emitting devices are generally less efficient than multi-layer organic light emitting devices. Recent EL research results indicate that those devices including only a single mixed layer of a hole transport material (composed of NBP, a naphthyl-substituted benzidine derivative) and an emitting electron transport material (composed of Alq3, tris(8-hydroxyquinoline) aluminum) are inherently believed to be unstable. The instability of these devices is believed to be caused by the direct contact between the electron transport material in the mixed layer and the hole injecting contact comprised of indium tin oxide (ITO), which results in the formation of the unstable cationic electronic transport material, and the instability of the mixed layer/cathode interface, see, H. Aziz et al., Science 283, 1900 (1999), the disclosure of which is totally incorporated herein by reference in its entirety.
Also, there have been attempts to obtain electroluminescence from organic light emitting devices by introducing a hole transport material and an emitting electron transport material as dopants in an inert host material, as reported in the above-described article by J. Kido et al. However, such known devices have been found to be generally less efficient than conventional devices including separate layers of hole transport material and emitting electron transport material.
While recent progress in organic EL research has perhaps elevated the potential of organic EL devices, the operational stability of current available devices may still be below expectations. A number of known organic light emitting devices have relatively short operational lifetimes before their luminance drops to some percentage of its initial value. Although known methods of providing interface layers as described, for example, in S. A. Van Slyke et al., xe2x80x9cOrganic Electroluminescent Devices with Improved Stability,xe2x80x9d Appl. Phys. Lett. 69, pp. 2160-2162, 1996, and doping, as described in, for example, Y. Hamada et al., xe2x80x9cInfluence of the Emission Site on the Running Durability of Organic Electroluminescent Devicesxe2x80x9d, Jpn. J. Appl. Phys. 34, pp. L824-L826, 1995, may perhaps increase the operational lifetime of organic light emitting devices for room temperature operation, the effectiveness these organic light emitting devices deteriorates dramatically for high temperature device operation. In general, device lifetime is reduced by a factor of about two for each 10xc2x0 C. increment in the operational temperature. Moreover, at these high temperatures, the susceptibility of the organic light emitting devices is increased as described, for example, in Zhou et al., xe2x80x9cReal-time observation of temperature rise and thermal breakdown processes in organic LEDs using an IR imaging and analysis systemxe2x80x9d, Advanced Materials 12, pp 265-269, 2000, which further reduces the stability of the devices. As a result, the operational lifetime of known organic light emitting devices at a normal display luminance level of about 100 cd/m2 is limited, for example, to about a hundred hours or less at temperatures in the range of about 60xc2x0 C. to about 80xc2x0 C., reference J. R. Sheats et al, xe2x80x9cOrganic Electroluminescent Devices,xe2x80x9d Science 273, pp. 884-888, 1996, and also S. Tokito et al., xe2x80x9cHigh-Temperature Operation of an Electroluminescent Device Fabricated Using a Novel Triphenlamine Derivative,xe2x80x9d Appl. Phys. Lett. 69, 878 (1996).
The present invention in embodiments overcomes or minimizes the above disadvantages of a number of known organic EL devices, which disadvantages primarily relate to device shorting at high temperatures, and which embodiments provide organic EL devices with enhanced stability at these temperatures. High temperature refers, for example, to above 60xc2x0 C., and specifically in the range of about 70xc2x0 C. to about 100xc2x0 C., or higher, such as, for example 120xc2x0 C. The present invention also embodies an organic EL device that contains at least one thermal protective element, for example up to four elements, and preferably one or two, wherein the thermal protective element is comprised of a single layer or a plurality of stacked layers laminated in contact to each other, and typically up to three layers. The thermal protective element(s) can be laminated in between or on top the other components (layers) of the organic light emitting device. The thermal protective element(s), for example, increase(s) the device resistance to shorting at elevated temperatures, and thus improves the thermal stability thereof.
Aspects of the present invention relate to an organic light emitting device comprising in sequence
a substrate;
a first electrode;
a light emitting region comprising an organic luminescent material; and
a second electrode; an organic light emitting device wherein one of the first electrode and second electrode serves as an anode, and one of the first electrode and second electrode serves as a cathode, and at least one thermal protective element; an organic light emitting device wherein the thermal expansion coefficient of the thermal protective layer is from about 1xc3x9710xe2x88x9210 meter/meter per degree Centigrade to about 9xc3x9710xe2x88x926 meter/meter per degree Centigrade, and wherein one of the first electrode and second electrode serves as an anode, and one of the first electrode and second electrode serves as a cathode, and wherein at least one thermal protective element is from about 1 to about 4 layers; an organic light emitting device wherein the thermal expansion coefficient of the thermal protective element or layer is from about 1xc3x9710xe2x88x9210 meter/meter per degree Centigrade to about 4xc3x9710xe2x88x926 meter/meter per degree Centigrade, and wherein one of the first electrode and second electrode serves as an anode, and one of the first electrode and second electrode serves as a cathode, and wherein at least one thermal protective element is a single layer; an organic light emitting device wherein the thermal protective element or layer is situated on the first electrode, on the second electrode and/or on the light emitting region comprising an organic luminescent material, and wherein one of the first electrode and second electrode serves as an anode, and one of the first electrode and second electrode serves as a cathode; an organic light emitting device wherein the thermal protective element is formed of a plurality of adjacent thermal protective layers, and wherein the individual thermal protective layers are comprised of similar or different materials; an organic light emitting device wherein the thickness of the thermal protective element is from about 10 nanometers to about 100,000 nanometers, and wherein one of the first electrode and second electrode serves as an anode, and one of the first electrode and second electrode serves as a cathode; t an he organic light emitting device wherein the thickness of the thermal protective element is from about 1 nanometer to about 10 nanometers, and wherein one of the first electrode and second electrode serves as an anode, and one of the first electrode and second electrode serves as a cathode; the organic light emitting device wherein the thickness of each of the individual thermal layers is from about 1 nanometer to about 2,000 nanometers; an organic light emitting device wherein there is from about 2 to about 4 thermal protective elements or layers; an organic light emitting device wherein the thermal protective element, layer, or layers is comprised of the same or different materials; an organic light emitting device wherein the thermal protective element, layer, or layers is coated on the second electrode; an organic light emitting device wherein the thermal protective element is comprised of a material selected from the group consisting of organic compounds, inorganic compounds, metals, metal alloys, and mixtures thereof; and optionally wherein the thermal expansion coefficient of this material is from about 1xc3x9710xe2x88x9210 meter/meter per degree Centigrade to about 9xc3x9710xe2x88x926 meter/meter per degree Centigrade; an organic light emitting device wherein the organic compound is copper phthalocyanine; an organic light emitting device wherein the inorganic compound is a metal compound selected from the group consisting of metal oxides, metal halides, metal carbides and metal nitrides; an organic light emitting device wherein the metal oxide is selected from the group consisting of MgO, Al2O3, BeO, BaO, AgO, SrO, SiO, SiO2, ZrO2, CaO, Cs2O, Rb2O, Li2O, K2O and Na2O; and the metal halide is selected from the group consisting of LiF, KCl, NaCl, CsCl, CsF and KF; an organic light emitting device wherein the metal compound is a silicon compound; an organic light emitting device wherein the silicon compound is SiO, or SiO2; an organic light emitting device wherein the metal is selected from the group consisting of Cr, Ti, Si, Ir, Pt, Os, V, Mo, Si, Zr, Ta, W, and Sb; and wherein the metal alloy is selected from the group consisting of Ni, Fe, Cr, Ti, Si, Ir, Pt, Os, V, Mo, Si, Zr, Ta, W, and Sb alloys; an organic light emitting device wherein the thermal protective element is comprised of a carbon compound; the organic light emitting device wherein the light emitting region comprises a hole transport region adjacent to the first electrode and which region is comprised of a hole transport material, and an electron transport region adjacent to the second electrode and comprised of an electron transport material, and wherein at least one of the hole transport region and the electron transport region emits light, and wherein one of the first electrode and second electrode serves as an anode, and one of the first electrode and second electrode serves as a cathode, and at least one thermal protective element situated on the cathode, the anode, or the cathode and the anode; an organic light emitting device wherein the light emitting region comprises a hole transport region adjacent to the first electrode and which electrode is an anode, and which region is comprised of a hole transport material; an electron transport region adjacent to the second electrode and which electrode is a cathode, and which electron transport is comprised of an electron transport material and the light emitting layer situated in between the hole transport region and a electron transport region comprised of an organic luminescent material, and further including a protective thermal element coated on the anode, the cathode, or the anode and the cathode; an organic light emitting device wherein the light emission region comprises a mixed region comprising a mixture of a hole transport material and an electron transport material, and wherein one of the first electrode and second electrode serves as an anode, and one of the first electrode and second electrode serves as a cathode, and further including at least one thermal protective element; an organic light emitting device wherein the light emission region comprises a mixed region comprising a mixture of a hole transport material and an electron transport material; and the light emitting region further comprises at least one of (i) a hole transport region interposed between the first electrode and the mixed region; and (ii) an electron transport region interposed between the second electrode and the mixed region, and wherein at least one of the hole transport region, the electron transport region and the mixed region emits light, and wherein one of the first electrode and second electrode serves as an anode, and one of the first electrode and second electrode serves as a cathode, and further including at least one thermal protective element coated on the anode or the cathode; an organic light emitting device wherein the light emission region comprises a component selected from the group consisting of polyphenylenes, polyphenylvinylenes, polyfluorenes, polypyrroles, polyanilines, and polythiophenes; an organic light emitting device wherein the light emitting region comprises a material selected from the group consisting of metal oxinoids, aromatic tertiary amines, indolocarbazoles, triazines, stilbenes, anthracenes, oxadiazole metal chelates, and porphyrins; an organic light emitting device wherein the hole transport component is selected from the group consisting of aromatic tertiary amines and indolocarbazole compounds, and the electron transport material is selected from the group consisting of metal oxinoids, triazines, stilbenes, and oxadiazole metal chelates; the organic light emitting device wherein the hole transport material is selected from the group consisting of N,Nxe2x80x2-di-1-naphthyl-N,Nxe2x80x2-diphenyl-1,1xe2x80x2-biphenyl-4,4xe2x80x2-diamine, 5,11-di-naphthyl-5,11-dihydroindolo[3,2-b]carbazole, and 2,8-dimethyl-5,11-di-naphthyl-5,11-dihydroindolo[3,2-b]carbazole, and the electron transport material is tris(8-hydroxyquinoline) aluminum or bis(8-hydroxyquinolato)-(4-phenylphenolato)aluminum; an organic light emitting device wherein the second electrode comprises at least one material with work function of not more than about 4.5 eV; an organic light emitting device wherein the second electrode is a cathode possessing a work function of not more than about 4.5 eV, and which cathode is selected from the group consisting of Li, Ca, Al, Mg, In, Ag, Mgxe2x80x94Ag alloys, Mgxe2x80x94Al alloys and Alxe2x80x94Li alloys; an organic light emitting device comprising in sequence
a glass substrate;
a first electrode anode comprised of, for example, indium-tin-oxide with thickness of from about 30 to about 300 nanometers;
a light emitting region situated on and in contact with the anode comprising a hole transport material selected from the group consisting of N,N-di-1-naphthyl-N,Nxe2x80x2-diphenyl-1,1xe2x80x2-biphenyl-4,4xe2x80x2-diamine, 5,11-di-naphthyl-5,11-dihydroindolo[3,2-b]carbazole, and 2,8-dimethyl-5,11-di-naphthyl-5,11-dihydroindolo[3,2-b]carbazole, and an electron transport material selected from the group consisting of tris(8-hydroxyquinoline) aluminum and bis(8-hydroxyquinolato)-(4-phenylphenolato)aluminum, and wherein the thickness of the light emitting region is from about 10 nanometers to about 300 nanometers; a cathode situated on and in contact with the light emitting region comprised of Al, Mgxe2x80x94Ag or Alxe2x80x94Li alloy of thickness from about 50 nanometers to about 500 nanometers; and a thermal protective layer or layers comprised of SiO, SiO2 or mixtures thereof of a thickness of from about 100 nanometers to about 1,000 nanometers; an organic light emitting device wherein the thermal protective layer mixture comprises from about 0.1 to about 99.9 weight percent of SiO, and from about 99.9 to about 0.1 weight percent of SiO2, and wherein the total thereof is about 100 percent; an organic light emitting device wherein the light emitting region includes a layer of a thickness of from about 10 nanometers to about 100 nanometers comprised of a mixture of from about 25 weight percent to about 75 weight percent of a hole transport material, and from about 75 weight percent to about 25 weight percent of an electron transport material; an organic light emitting device further containing a thermal protective element formed of a single layer or a plurality of stacked layers laminated in contact to each other; an electroluminescent device comprised of an optional supporting substrate, a first electrode, a second electrode, a light emitting region, and at least one thermal element; and an electroluminescent device wherein the thermal protective element is a layer, a plurality of layers, or a plurality of laminated layers, the first electrode is an anode, and the second electrode is a cathode, and the element is contained on the anode, or the cathode.
The thermal protective element(s) comprise(s), for example, a material having a thermal expansion coefficient such that the resistance of the device to shorting at elevated or high temperatures is reduced. A typical range for the thermal expansion coefficient can be, for example, from about 1xc3x9710xe2x88x9210 meter/meter per degree Centigrade to about 9xc3x9710xe2x88x926 meter/meter per degree Centigrade, and preferably from about 1xc3x9710xe2x88x9210 meter/meter per degree Centigrade to about 4xc3x9710xe2x88x926 meter/meter per degree Centigrade. Examples of materials that can be selected for the thermal protective element include, for example, organic compounds like porphyrins, such as copper phthalocyanine; inorganic materials like metal compounds, such as SiO, SiO2, ZrO2, Si3N4 and SiC; and metallic materials like pure, about 99 to 100 percent pure metals, such as Cr, Ti, Si, Ir, Pt, Os, V, Mo, Si, Zr, Ta, W and Sb, and metal alloys, such as Nixe2x80x94Fe alloys, Nixe2x80x94Cu, KOVAR(copyright) and Crxe2x80x94Fe alloys. KOVAR(copyright) contains about 53 weight percent Fe, about 17 weight percent Co, about 29 weight percent Ni, about 0.2 weight percent Si, about 0.3 weight percent Mn, and about 0.02 weight percent carbon. The thickness of the thermal protective element, layer, or layers can vary and can be, for example, from about 1 nanometer to about 100 microns.
The organic EL devices according to embodiments of the present invention can be utilized in various applications, such as displays like screens of TVs, computers, and some handheld personal electronic devices, such as cellular phones, and which devices that are operated or stored over a broad temperature range, such as from about 25xc2x0 C. to about 100xc2x0 C.; wherein the organic EL devices are exposed to elevated temperatures of, for example, from about 70xc2x0 C. to about 100xc2x0 C., or higher, and wherein the adverse effects at these elevated temperatures on device performance, such as device shorting, are minimized or avoided. Examples of these applications include, for example, when it is desirable to thermally anneal the organic EL devices to achieve certain properties, reference copending application U.S. Ser. No. 09/629,163 (D/A0057), the disclosure of which is totally incorporated herein by reference, or wherein exposure of the organic EL device to elevated high temperatures is unavoidable.